Marine seismic data acquisition and processing generates a profile (image) of a geophysical structure under the seafloor. Reflection seismology is a method of geophysical exploration to determine the properties of the Earth's subsurface, which is especially helpful in determining an accurate location of oil and gas reservoirs. Marine reflection seismology is based on using a controlled source of energy—typically acoustic energy—that sends the energy through subsurface geologic formations. The transmitted acoustic energy propagates downwardly through the subsurface as acoustic waves, also referred to as seismic waves or signals. By measuring the time it takes for the reflections or refractions to come back to seismic receivers (also known as seismic data recorders or nodes), it is possible to evaluate the depth of features causing such reflections. These features may be associated with subterranean hydrocarbon deposits.
There are many methods to record the reflections from a seismic wave off the geological structures present in the surface beneath the seafloor. In one method, a marine vessel tows an array of seismic data recorders provided on streamers. In another method, seismic data recorders are placed directly on the ocean bottom by a variety of mechanisms, including by the use of one or more of Autonomous Underwater Vehicles (AUVs), Remotely Operated Vehicles (ROVs), or by dropping or diving from a surface or subsurface vessel. In either method, the data recorders can be discrete, autonomous units (no direct connection to other nodes or to the marine vessel) where data is stored and recorded or integrally linked (via communications and/or power) via wire or wireless links (such as acoustic, electromagnetic, or optical links).
Autonomous ocean bottom nodes are independent seismometers, and in a typical application they are self-contained units comprising a housing, frame, skeleton, or shell that includes various internal components such as geophone and hydrophone sensors, a data recording unit, a reference clock for time synchronization, and a power source. The power sources are typically battery-powered, and in some instances the batteries are rechargeable. In operation, the nodes remain on the seafloor for an extended period of time, which may last up to 6 months or longer. Once the data recorders are retrieved, the data is downloaded and batteries may be replaced or recharged in preparation of the next deployment.
The ocean bottom node is typically self-sealing and leak proof and is safeguarded against temperature and pressure variations present at the bottom of the ocean. The typical battery used in such nodes is contained within the node's housing, and the housing or case of the node must be removed or opened to retrieve the battery after the node has been retrieved and brought to the ocean surface. Whether the battery is rechargeable or replaceable, the battery is connected via direct electrical or wire connections to other components of the node.
There are several problems with current battery configurations for seismic nodes. For example, common batteries in a seismic node generally involve conductor contacts between the battery and the node electronics. The conductor contacts may become corroded or worn through repeated removal and replacement of batteries and in response to moisture leakage. If the batteries are rechargeable, charging typically requires a wired charge connection, which means that the nodes cannot be deployed for up to several hours while the batteries are charged. Also, typical node configurations do not allow for simple automation of the recharging process. When several nodes are recharged simultaneously, it may require a complex system of wires for connecting the nodes, etc. One of ordinary skill will recognize several additional problems with common battery configurations in seismic nodes.